1. History of the Invention
The present invention relates to magnetic head assemblies, and more particularly to magnetic head assemblies having a read/write head mounted in a ceramic slider body and straddled by an opposite pair of erase core elements.
2. History of the Prior Art
Advancing technology in the magnetic recording area has resulted in various noncontact recording schemes to provide various advantages such as higher data transfer rates. In such schemes the head assembly is supported by a self-acting sliding or air bearing relative to a moving record member such as a magnetic disk. The disk itself may be of the rigid type, or it may be flexible. With rigid disk systems the head is "flown" above the disk on an air bearing layer which may be small but is still measurable and the magnetic interchange is effected by noncontact recording. In the great majority of flexible disk systems the spacing is much more intimate and the magnetic interchange is referred to as being effected by contact, even though a very thin film of air may exist between the head and disk.
In flexible disk systems such as those in which the magnetic medium comprises a flexible Mylar substrate having magnetic layers (the so-called "floppy" disks) to provide the recording surfaces, the magnetic read/write transducers are disposed very close to or in contact with the recording surfaces even though mounted in a fluid bearing type of slider body. To limit the width of the track written by the read/write transducers, the magnetic head assembly may include erase transducers positioned on opposite sides of the read/write transducer to erase the edges of the track immediately after it is written. An example of such a magnetic head assembly which is commonly referred to as a straddle erase head is provided by U.S. Pat. No. 3,964,103 to Thompson et al.
In the Thompson et al patent the magnetic head assembly is made from a ceramic slider having a pair of orthogonal slots and a trough therein. After a read/write core and a pair of erase pole pieces are placed in the opposite slots and glass rods are placed in the trough, the assembly is heated to melt the glass and bond the core and pole pieces in place prior to installation of coils and a side bar to complete the magnetic circuit. In still other prior art arrangements the straddle erase pole pieces are mounted in place within a slider assembly using other materials and techniques such as epoxy bonding.
While prior art straddle erase head assemblies have provided a reasonably effective way of storing and retrieving information from recording mediums such as a flexible magnetic disk, such assemblies suffer from a number of problems. One problem is the relatively high cost of the head assemblies stemming from the need to use individual head assembly processes. Other factors contributing to high cost include the cost of components such as erase elements and the low yields involved even though heads commonly assembled individually.
Of at least equal importance to the problems of assembly costs are those relating to accurate dimensioning and positioning of the various elements within the head assembly. These heads, and their component parts, are now extremely small and dimensional tolerances and part alignment represent significant quality control problems. The width of the erase head and the dimension of the erase gap must desirably be controlled within ranges measured in ten thousandths of an inch and microinches respectively. Poor control of the length of the erase gap between the read/write core and the erase core element is a common problem resulting from conventional fabrication techniques and one which can seriously affect the performance of the head assembly. Although there is some disparity in usage of the term within the industry, the "erase gap length" is here referred to as the dimension transversely across the non-magnetic spacer in the erase head. A related problem involves poor control of the erase track width between the read/write core and the opposite edges of the erase core elements. Coupled with this problem is an inability to easily and therefore economically adjust the erase track width to accommodate different track densities. Further problems relate to precise definition and capability for adjustment of the erase gap height.
Most such dimensioning and positioning problems in conventional straddle erase heads result from head assembly designs and fabrication techniques which do not permit positive control over such parameters. For example, assembly methods such as the one disclosed in the Thompson et al patent which utilize glass bonding typically rely on gravity during the bonding process to hold the various core elements in place. As the glass becomes molten the core elements are often lifted out of place and tend to remain somewhat out of place as the glass hardens. The resulting displacement can seriously affect erase gap length and height and erase track width as well as other head assembly parameters. Any skewing or misalignment of one component relative to the others adversely affects the head characteristics, and does so in a way which results in undesirable variations in the manufactured heads. Similar problems arise where the various core elements are bonded in place using epoxy or other adhesives.
Accordingly, it would be advantageous to provide methods of making straddle erase magnetic head assemblies which are economical and which readily lend themselves to batch fabrication techniques.
It would furthermore be advantageous to provide straddle erase head assemblies and methods of making the same which provide for the positive control of parameters such as erase gap length and height and erase track width, while at the same time permitting substantial variation in such parameters, if desired to meet different application requirements.